Corrosion prevention method



CORROSION PREVENTION METHOD Richard S. Treseder, Oakland, and Philip J. Raifsnider,

Richmond, Calif., assignors to Shell Development Company, Emeryville, Calif., a corporation of Delaware No Drawing. Application February 2, 1953, Serial No. 334,726

9 Claims. (Cl. 252-855) This invention relates to a method of corrosion-inhibition of a ferruginous material, e. g., steel, while in contact with an agitated fluid system of liquid or liquefied phases and an atmosphere of aqueous carbonic acid and/or carbon dioxide. More particularly, the invention applies to corrosion-prevention'of metal equipment normally used in operating gas-condensate light gasoline wells, whereby such corrosion-prevention is effected during the conventional operation of these wells.

In recent years, the problem of preventing corrosion of ferruginous materials in the systems indicated above has become very serious. No entirely satisfactory method is known for preventing corrosion of tubing in operating wells under the corrosive conditions indicated above.

It is an object of the present invention to provide an inexpensive and industrially feasible method of corrosioninhibition of ferruginous metals in a system in which an agitated flowing mixture of non-oxidizing gases, a liquefied hydrocarbon phase and an aqueous carbonic acid phase come in contact with such ferruginous metal. It is another object to overcome the disadvantages of prior art practices peculiar to corrosion-inhibition applied in operation of gascondensate wells. A further object is to provide an inexpensive and industrially feasible corrosioninhibition treatment of iron-containing metals contacting the above-specified system as it occurs in the base of an operating gas-condensate well.

Now in accordance with the present invention, it has been found that corrosion which is caused by contact of ferruginious metal with a system of non-oxidizing gases, with an agitated flowing mixture of a liquefied hydrocarbon phase, and with an aqueous carbonic acid phase, can be inhibited by introducing thereinto (continuously or intermittently), a minor but corrosion-inhibiting amount of a mixture of sticking residue sulphates (apparently alkyl ammonium sulfates) originally existing in the acid sludge which results from the treatment or alkylation of petroleum fractions (especially, petroleum distillates) with concentrated sulfuric acid as more particularly described hereinafter. Further, in accordance with the present invention, it has been noted that is such sulfates in their form as extracted from acid sludge are stored or transported in ferruginous containers, such as drums or the like, while in a relatively concentrated state, corrosion may occur prior to the time at which the sulfates are mixed with the rising condensate stream in the oil well. In correcting this shortcoming, it has been found that the addition of a metallic nitrite to the concentrated sulfate mixture followed by heating thereof within a stated temperature range results in a concentrated reaction mixture which exhibits no adverse corrosive effect toward ferruginous containers and which, moreover, exhibits highly satisfactory protective effects when utilized in the proper concentration in gas-condensate wells.

The liquefied hydrocarbon phase in gas-condensate wells normally comprises mixtures of liquid methane, ethane, propane, butane and heavier hydrocarbon condensates up to and including light gasolines having up to nited States Patent C) ice about eight carbon atoms. Normally gaseous hydrocarbons are partly liquefied in the well because of the pressures ordinarily existing therein. A typical gas-condensate well produces between five and thirty barrels of a liquefied hydrocarbon phase per million cubic feet of gas (MMCF), at a typical well-head temperature and pressure. The temperatures at the bottom of the well usually range from about 85 C. to to about 125 C., average temperatures at the well-head being usually in the range from about 45 C. to about 80 C. Pressures in a condensate well usually range from about 1,000 to about 7,000 pounds per square inch absolute. A typical well may have a bottom-hole pressure of about 2,700 p. s. i. a. and a flowing tubing pressure of about 2,000 p. s. i. a. The pressure increases the ratio of gaseous carbon dioxide (present in condensate wells) which will dissolve in the aqueous phase also present therein. At well-head condicarbon phase and gases is usually distributed throughout nents found in the sludge resulting from acid treatment the flowing system of the well. V

The inhibitor is indeterminate in character with respect to the isolation of identifiable members. This is, of course, due to the highly complex nature of the compoor alkylation petroleum products.

A typical process for recovery of the desired amine sulfates comprises the following steps: Acid sludge, such as that derived by treatment of gas oil with concentrated sulfuric acid, is contacted with ammonia in the presence of water to form an aqueous ammonium sulfate solutionj treating at least a portion of (i. e. l0l00%) said solution with petroleum nitrogen bases (3-10% by volume) whereby complexes are formed between said bases and the desired organic sulfates; displacement of the bases from the complex by treatment with ammonia, thus obtaining the organic ammonium sulfates.

It will be understood that the precise source of the acid sludge and the particular process for the isolation of the subject inhibitors therefrom do not constitute a part of the present invention. One process for such isolation is described in U. S. Patent 2,331,235 to J. D. Ruys wherein the desired inhibitors are referred to as sticky residue. The described process is especially suitable for extraction of alkylation acid sludges, but may also use petro leum product treating acid sludges as well, wherein the treatment has been either sulfonation or removal of unsaturates, such as the acid treatment of pressurev distillates and the like. Other bases instead of ammonia may be employed, such as sodium, potassium or calcium hy droxides. The nitrogen bases capable of forming complexes with the inhibitor may be those isolated from the sludge, such as taught by the Ruys patent. Alternatively,

bases such as the picolines or quinolines may be used.

Acid sludges contain a complex mixture of sulfuric.

acid, water, sulfur dioxide, sulfonic acids, nitrogen bases,

wherein R is an alkyl radical having from about-3 to about 12 carbon atoms, and usually from about 4 to 1: about 8 carbon atoms; The subject sulfates are 'subst'an" tially water dispersable, or soluble in aqueous ammonium sulfate solutions.

Particularly significant corrosion-prevention in the practice,of.the.invention has-been obtained with the waterdispersible sulfates obtained from the above-described sourcesat concentrations belowabout 1% by'weight of the aqueous phase-in the gas-condensate well but preferably. above about 0.01% by weight thereof.

vItisnot known just how the present class of inhibitors act .to prevent corrosion of steel under the conditions employed in the present invention. Suifice it to say that they have been-found to. act eifectively. This is surprising, in view of the turbulence offlow in the'system and the low concentrations of inhibitor (less'than about lwt. percent, based on the liquefied hydrocarbon phase) which areelfcctive relative to the muchhigher concentrations of carbonic acid andother dispersing components in the system. Also, thesev inhibitors are sensitive to the liquefied hydrocarbon :phase; so it would seem that they would be swept .away by the turbulence flow of this phase, leavingthe. surface of the metal open to attack by the swiftly churning aqueous carbonic acid present.

The present agents may beintroduced intogas-condensate wells'in various ways. :For'example, tubing of relatively small diameter maybe run down through the production tube of such a well'to approximately the bottom end thereof, and a solution of the present agents may be pumped through the small-diameter tubing so as to enter the well streamnear the bottom of the well tube; thev risingturbulent flow will then carry the injected agent up through the tube. Obviously, the corrosion inhibitors maybe added to or introduced into the wells by other means or methods depending, in part, on whether the wells are operated .through the casings. or through tubing disposedin such casings. Also, it is clearthat the inhibitors may be introduced into the top of the well and allowed to flow down, or may be forced to any given point or points. in the well, at which the inhibitor then can come in contact with the turbulent up-fiowing fluid mixture which, as stated, would. cause metal corrosion but for the presence of the corrosion inhibitors of this invention. The inhibitor may be mixed with 10-100% of petroleum waxes to.form a .solid composition which may be dropped in the well in the form of granules, cubes or sticks.

The employment of the present agents is best effected by having themin solution in an aqueous medium readily miscible with the aqueous phase of the well system, and then introducing the solution of the agent or agents to a condensate well as above-described. Any solvent which is .-substantially non-reactive with'the agents'under the conditions employed (e. g., such solvents as esters, alcohols,.ketones, etc.) may be used for preparing an inhibitor solution, although his preferable to employ water. In some cases it is advantageousto use a more or less concentrated solution or dispersion (as up to about 50 wt. per cent of the agent(s)) in a suitable fluid medium. The amount of solvent in the inhibitor solution is so small, relative to the volume of liquid in the system treated therewith, that it does not materially affect the normal operation of the well.

For purposes of further illustration, reference willnow bemade to thefollowing examples, it being understood thatnthereis no intention of being limited necessarily to the specific conditions disclosed therein. In these examplessteel plates.(% inch width, inch length, sandblasted coldrolled steel strips) were placed inglass oilsarnple bottles containing g. of a water solution having 3% wt percent .of sodium chloride, 0.1%'wt. CaClz, 0.03% .MgClz, 0.1% .acetic acidand 50 ml. of kerosene containing in some cases the additive of the present invention, obtained from alkylation acid sludge. The concentration of the additive was based upon the water content. .The .contentspof each bottle were then saturated withzrarbon dioxide ggas as follows: Air was displaced by passing carbon dioxide to the bottom of each bottle for approximately 10 minutes. The prepared bottles were then tightly closed and the stoppers wired on to withstand the pressure developed at elevated temperatures. The bottles were then rotated end-over-end at 60 R. P. M. at a temperature of approximately C. for a period ranging from 18 to 24 hours. At the end of this time the corrosion rates were measured for each steel plate. The results obtained by followingthe-above-described technique are given below:

Example I A series of steel plates were subjected to the above treatment in a container having 50ml. of kerosene and 10 ml. of water, the-latter containing 3% by weight of sodium chloride, 0.1 CaCl2,-0.1% w. acetic acid and 0.03% w. MgClz. No corrosion inhibitor was present. An analysis of the thus treated plates showed that the average corrosion rate was aboutSOmils per year.

Example 11 Steelplates'of the abovetype were treated in the same manner in the presence of sulfates isolated from acid sludge resulting from the treatment of west coast petroleum distillates. The inhibitor was utilized in amounts of 0.05'%,'.011% and'0.'2% by weight of the water phase. Aftertreatment the plates showed that the-corrosion resulting from the use of such inhibited combinations was in the order of 10,8 and 7 milspenyear, respectively. Consequently, it will'beseen'that the rate of corrosion was reduced-sharply when the complex mixture of amine sulfates was utilized.

' Example III Utilizing the information gained, inthe above-described laboratory .experiments, field-trials were instituted in which the complexinhibitor wasintroduced periodically into the annulusbetween the well .casing and the well tubing. The .well' being treated was'one producing approximately 4.6,million ,cubic feet gas and condensate per day; .Thewell was yielding approximately 10 barrels of salt water atzthe same'time. The corrosion rate of the test; panelsexpose'd in.the. floor. line of the well dropped from mils .per year whenthe well was uninhibited to about 10-milszper-year at therend of a six-weeks period, the injection rate being .about-0.4 .quart-of inhibitor per million cubic feet-of .gas condensate, or about 0.12% based on thewater phase.

Example IV Due tothe occurrence of a certain amount of corrosion in iron drums in which the concentrated inhibitor was stored and :transported, .the amine sulfate mixture was modified by the following process:

3215.1bs. of fsticky residue organic ammonium sulfatesfrom refinery acid -sludge,,having a-pH of 2.0, was neutralized to-pHof 6.8 by the addition of 89 lbs. of anhydrous ammonia. Sodiumnitrite amounting to lbs., or 6% by weight of the charge, was then added and the mixture stirred at 5560 C.-for :17 hours. Following this'reactionperiod (during which a portion of the sodium nitrite was .converted to "nitrous acid) the charge was cooled without stirring and settled for four days. A lowerphase consisting mainly of ammonium sulfate was .run off to waste-while the upper oily phase, weighing 2615 lbs., was transferred-to-drums. The resulting concentrated and inhibited mixture of amine sulfates exhibited no corrosion of the iron drums during an extended storage and-shipping period.

The treatment of the sludge sulfates derived from petroleum refineryacidsludges preferably comprises the addition of between about 0.1 and about 50% of a metallic nitrite based on .the-weight of.concentrated .amines, ,said concentrated amines constituting approximately between about,l0%-;andzabouts80%.:of sludge sulfates. In order to produce the :desired reaction between the ,nitrite and the crude sulfate mixtureheating is preferably conducted at temperatures between about 40 C. and 80 C. for periods of between about one-half hour and 72 hours. The resulting mixture preferably contains a residual amount of sodium nitrite in the order of about .01-2.0% based on the concentrated amine sulfates, the remainder having been converted to nitrous acid which eventually is dispersed from the system in the form of nitrogen oxides and water. This inhibited concentrate was then employed in a well injection as described in the previous example to obtain a substantial reduction in corrosion.

We claim as our invention:

1. The method of treating a hydrocarbon-containing system in its natural state in a well for the purpose of inhibiting corrosion by aqueous carbonic acid of well metal parts, said system comprising a non-oxidizing gas phase,

a liquefied normally gaseous hydrocarbon phase and a minor amount of aqueous carbonic acid, which system in a state of agitated flow at a temperature of between about 45 C. and about 125 C. and under a pressure of between about fifteen and seven thousand pounds per square inch absolute, comes in contact with corrodible well parts, which method includes the step of mixing with said system an amount of below approximately one weight per cent and above approximately 0.0001'weight per cent of the liquid hydrocarbon phase contacted, of water soluble ammonium salts of organic sulfuric acids isolated from petroleum refinery acid sludge.

2. The method of treating a hydrocarbon-containing system in its natural state in a well for the purpose of inhibiting corrosion by aqueous carbonic acid of well metal parts, said system comprising a non-oxidizing gas phase, a liquefied normally gaseous hydrocarbon phase and a minor amount of aqueous carbonic acid, which system in a state of agitated flow at a temperature of between about 45 C. and about 125 C. and under a pressure of between about fifteen and seven thousand pounds per square inch absolute, comes in contact with corrodible well parts, which method includes the step of mixing with said system an amount of below about 1% by weight and above about 0.0001% by weight of the aqueous phase contacted of water-dispersible ammonium salts of organic sulfuric acids, said sulfates being those recovered from the acid sludge resulting from the sulfuric treatment of petroleum distillates, said sulfates also containing between about 0.01% and about 2.0% by weight thereof of a metallic nitrite.

3. A process according to claim 2 wherein the nitrite is an alkali metal nitrite.

4. A process according to claim 2 wherein the nitrite is sodium nitrite.

5. A process according to claim 1 wherein the acid sludge is that resulting from the alkylation of petroleum distillates with sulfuric acid.

6. A process according to claim 1 wherein the ammonium salts are those obtained by the treatment of petroleum distillates in the kerosene and gas oil ranges with sulfuric acid for the removal of unsaturated hydrocarbons.

7. The method of treating a hydrocarbon-containing system in its natural state in a well for the purpose of inhibiting corrosion by aqueous carbonic acid of Well metal parts, said system comprising a non-oxidizing gas phase, a liquefied normally gaseous hydrocarbon phase and a minor amount of aqueous carbonic acid, which system in a state of agitated flow at a temperature of between about C. and about 125 C. and under a pressure of between about fifteen and seven thousand pounds per square inch absolute, comes in contact with corrodible well parts, which method includes the step of mixing with said system an amount of below about 1% by weight and above about 0.0001% by weight of the aqueous phase contacted of water-dispersible ammonium salts of alkyl sulfuric acids, said sulfates being those recovered from the acid sludge resulting from the sulfuric treatment of petroleum distillates, said sulfates also containing between about 0.1% and about 2.0% by weight thereof of a metallic nitrite.

8. A process according to claim 7 in which the alkyl radicals of the ammonium salts of alkyl sulfuric acids predominates in radicals having from 3 to 12 carbon atoms each.

9. In the method of improving the corrosion properties of water-dispersable ammonium salts of alkyl sulfuric acids, said salts being recovered from the acid sludge resulting from the sulfuric acid treatment of petroleum distillates, and said sulfates being corrosive in concentrated solution toward ferruginous metals, the steps comprising adding to said ammonium salts an amount between about 0.1 and about by weight of a metallic nitrite based on the crude salt mixture, said mixture comprising between about 10% and about by weight of ammonium salts, and heating the mixture of ammonium salts and nitrite at a temperature between about 40 C. and 80 C. for a period between about one-half and about 72 hours, the resulting mixture containing between about 0.01 and 2.0% by weight of metallic nitrite subsequent to said heating period.

References Cited in the file of this patent UNITED STATES PATENTS 2,331,235 Ruys et al Oct. 5, 1943 2,402,793 White et al June 25, 1946 2,582,733 Zimmer et a1. Jan. 15,1952 2,583,399 Wachter et al. Ian. 22, 1952 

1. THE METHOD OF TREATING A HYDROCARBON-CONTAINING SYSTEM IN ITS NATURAL STATE IN A WELL FOR THE PURPOSE OF INHIBITING CORROSION BY AQUEOUS CARBONIC ACID OF WELL METAL PARTS, SAID SYSTEM COMPRISING A NON-OXIDIZING GAS PHASE, A LIQUEFIELD NORMALLY GASEOUS HYDROCARBON PHASE AND A MINOR AMOUNT OF AQUEOUS CARBONIC ACID, WHICH SYSTEM IN A STATE OF AGITATED FLOW AT A TEMPERATURE OF BETWEEN ABOUT 45* C. AND 125* C. AND UNDER A PRESSURE OF BETWEEN ABOUT FIFTEEN AND SEVEN THOUSAND POUNDS PER SQUARE INCH ABSOLUTE, COMES IN CONTACT WITH CORRODIBLE WELL PARTS, WHICH METHOD INCLUDES THE STEP OF MIXING WITH SAID SYSTEM AN AMOUNT OF BELOW APPROXIMATELY ONE WEIGHT PER CENT AND ABOVE APPROXIMATELY 0.0001 WEIGHT PER CENT OF THE LIQUID HYDROCARBON PHASE CONTACTED, OF WATER SOLUBLE AMMONIUM SALTS OF ORGANIC SULFURIC ACIDS ISOLATED FROM PETROLEUM REFINERY ACID SLUDGE. 